A conventional dump vehicle includes a frame mounted on wheels and a bed that is configured to hold a volume of material to be transported and eventually dumped, such as gravel, sand, asphalt, etc. Via a hydraulic lifting mechanism, the bed is able to be inclined or "tipped" with respect to the frame to urge any material contained therein to be dispensed through the bed's discharge port, which is usually a rear opening. Dump vehicles of this type also include a gate that is pivotally coupled to the bed and is pivotal from a closed position, in which the gate closes the opening and prevents material from passing there through, and a pivoted position, in which the gate is swung away from the bed and allows material to be freely dispensed through the opening.
The gate is retained in its closed position by a pair of pivotal latches, or dogs, that extend over a pair of tabs, one extending outwardly from each lateral edge of the gate, to retain the gate against the rear portion of the bed. When the dogs are actuated, they pivot generally upwardly and away from the tabs to release the tabs and enable the gate to pivot outwardly from bed, thereby allowing the material contained therein to be dispensed through the rear opening. When the gate is in this pivoted position, the material in the bed may be dumped out of the bed simply by inclining the bed with respect to the frame. The material is dispensed rather quickly, in an unmetered fashion, through the opening and onto the ground or other surface proximate the vehicle.
Unfortunately, it is extremely difficult, although often necessary, to control the rate at which the material is dispensed. The speed of the vehicle, the angle of the bed with respect to the frame, and the viscosity of the material contained within the bed are factors which affect the rate at which material is dispensed from the gate and onto the ground. None of these factors, however, whether considered alone or collectively, enable sufficient control of the flow rate of material from the bed.
With the conventional dump vehicle described above, a chain is often used to attempt to control the degree to which the gate may pivot away from the rear opening, thereby controlling the rate at which material is dispensed from the bed. One end of the chain is secured to the frame or bed, and the chain is secured to the gate a specified distance from the secured end. By selecting a particular length of chain, usually a certain number of links, between the gate and the bed, the user is able to set a maximum angle at which the gate can pivot away from the bed. Unfortunately, this is a very rough measurement that lends itself to considerable guessing and speculation on the part of the user. Moreover, if the user guesses incorrectly, it is not possible to readjust the measurement. Similarly, it is not possible to adjust the measurement if the desired flow rate changes. Instead, once the material has begun to flow out of the rear opening, it will generally have sufficient weight to prevent the tailgate from being returned to the closed position until all, or at least most, of the material has been dispensed from the bed. It should be understood that this is not, as used herein, metered discharge of the material from the bed. While an upper limit to the flow rate of material from the bed may be established, the flow rate may not be adjusted or stopped.
Furthermore, once a flow of material from the bed has begun, it is not possible to stop the flow quickly, and often times is only possible after a majority of the material has been dispensed. At best, the bed can be returned to its most level position, and the material will continue to flow out of the opening until the outward force exerted on the pivoted gate by the material is less than the opposite force exerted by the gate on the material. Even when these forces are in equilibrium, the gate often cannot be returned fully to its closed position because of material trapped between the opening and the gate. This is especially true when the material is asphalt or rock.
Therefore, with a conventional dump vehicle and tailgate, it is possible to dump all of the material at once, or to make a one-time estimate and hope that the selected angle produces the desired flow rate of material through the rear opening. In addition, even if the desired flow rate is obtained, it is not possible to stop the flow of material through the rear opening until most or all of the material has been dispensed. Moreover, the flow of material generally spans the entire length of the rear opening and may not be selectively dispensed over only a variable portion of the length of the opening.
One attempt to solve this problem is disclosed in U.S. Pat. No. 4,989,918 to Biddy, which is entitled "Material Handling Vehicle with Improved Tailgate," the disclosure of which is hereby incorporated by reference. Biddy discloses a dump truck with a tailgate that may be raised with respect to the bed by a pair of hydraulic lifting members and subsequently pivoted outwardly from the bed. The truck includes a pair of channels extending upwardly from adjacent the floor of the bed into which the tabs on each side of the tailgate are retained until the gate is raised a defined distance above the floor of the bed. When the tabs are within the channels, the gate may be selectively raised or lowered to control flow of material through the rear opening of the bed. Once the gate is raised to a height at which the tabs are higher than the channels, the gate is free to swing outwardly from the bed for unmetered, or uncontrolled, dumping of the material through the rear opening.
The drawback to this design, however, is that the vehicle of Biddy does not enable the gate to, from a closed position, be either pivoted or raised with respect to the bed. Instead, the gate must always be raised, from a closed position, to a height that exceeds the height of the channels. Only at this point may the gate be pivoted with respect to the bed. Therefore, if the user desires to quickly dump the material contained within the bed, the user must wait while the gate is raised a distance equal to the height of the channels before the gate may swing outwardly from the bed.
An additional problem with the design of Biddy is that the system is entirely dependent upon the operation of the hydraulic lifting members. If either of the members fails or malfunctions, the gate is locked in its current position, and the truck is inoperable for its intended purpose until the member is repaired. For example, if either of the hydraulic members or the system providing power and fluid to the members fails when the gate is in its closed position, the gate is locked in this position, with the tabs firmly retained within the channels. Even if the lifting members could be disengaged, the gate would have to be manually raised to allow the material within the bed to be removed. In most applications, the weight of the material within the bed would make the process extremely difficult and time-consuming.
Another disadvantage is that the distance through which the gate may be raised and returned to a closed position is directly proportional to the time it takes to pivot the gate away from the bed. For example, if the channels are fairly long, then the user has a wide range of heights at which the level of the gate with respect to the bed may be positively controlled. However, the gate must be raised through this entire height in order to pivot the gate away from the bed. On the other hand, if the channels are relatively short, the gate may be raised more quickly to a sufficient height to be pivoted away from the bed, but the user will have a much more limited range of heights at which the elevation of the gate may be positively controlled. Therefore, there is a constant tradeoff between the time to pivot the gate away from the bed and range of heights within which the elevation of the gate may be positively controlled.
A further disadvantage of the vehicle disclosed in Biddy is the position of the channels with respect to the floor of the bed. Because the channels extend from below the floor of the bed and have internally oriented openings extending along their entire length, material dispensed from the bed will always be prone to being received within the channels. When the transported and dumped material is compressible and easily removed, this may be more of a recurring inconvenience than a serious disadvantage. When the material is substantially incompressible, such as rock or gravel, then any of the material that is received within either of the channels may prevent the gate from being returned fully to its closed position. It should be understood that if the gate cannot be returned to its closed position, then the discharge port or opening of the vehicle will not be closed fully, thereby allowing material to continuously flow out of the opening until the obstruction is removed. Furthermore, to remove the obstruction, the gate would most likely have to be raised with respect to the floor of the bed, thereby increasing the available size of the opening and allowing even more material to be dispensed and possibly introduced into the channels.
Even more problems are encountered when the material hardens over time from a fluid or relatively amorphous state to a solid state. An example of such a material is asphalt. If this material is received and allowed to harden within the channels, it is possible to lock the gate in a given position because the tabs are stuck in that position by the hardened material. It is also possible that the material will harden within the channel and prevent the gate from being fully closed because the material will obstruct the lower or other portion of the channel. Therefore, if the vehicle is going to be used with this type of material, the channels and tabs must be continuously monitored for any build-up of hardened material.
Although Biddy attempts to address and satisfy some of the above-recited problems inherent in a conventional dump vehicle, it is an unsatisfactory solution to these problems, for at least the reasons discussed above. Accordingly, it is a primary object of the present invention to provide a dump vehicle with a gate that may, from a closed position, be selectively pivoted away from the bed or raised with respect to the bed to respectively allow unmetered or metered discharge of material from the bed.
Another object of the invention is to provide such a vehicle with a dual-control mechanism that uses separate sets of mechanisms to cause the gate to be raised and to be pivoted with respect to the bed.
Still another object of the present invention is to provide a positively controlled tailgate system that may be easily and quickly retrofit on an existing dump vehicle.
Yet another object of the present invention is to provide such a system which utilizes a substantial amount of the existing components of the vehicle.
One more object is to provide such a vehicle and system that are durable and able to sustain the abuses encountered in their operating environment, while still being easy to maintain and requiring minimal maintenance.
Another object is to provide for selective control of the width, as well as the height, of the discharge port from the bed.
The invention achieves these and other objects and advantages in the form of a dump vehicle with a positively controlled opening gate. The vehicle includes a frame, a dump bed mounted on the frame and having a floor, front and side walls and a rear opening through which material can be discharged from the bed, and a gate having a pair of lateral edges and a lower edge. The gate is pivotally mounted adjacent the rear opening and has a closed position in which the gate blocks the rear opening to prevent discharge from the bed through the rear opening. The vehicle further includes a gate control mechanism connected to the gate. The gate control mechanism is adapted to selectively raise the gate from the closed position to allow metered discharge of material or to release the gate from the closed position so that the gate may pivot away from the rear opening to allow unmetered discharge of material.
These and other advantages and features of the invention will become more fully apparent as the detailed description below is read with reference to the accompanying drawings.